High-speed data communications cables currently in use include pairs of insulated conductors twisted together to form a two-conductor group or a transmission line. Such pairs of insulated conductors are commonly referred to in the art as “twisted pairs”. Multiples of twisted pairs are typically bundled or closely spaced together within high-speed data cables. Such close proximity between twisted pairs often causes electrical energy to transfer from one twisted pair to other adjacent twisted pairs coexisting within a cable. This transfer of electrical energy between twisted pairs is a phenomenon known as crosstalk, which interferes and degrades electrical signals and data transmission. Twisted pairs must, therefore, be sufficiently separated physically and shielded electrically in order to reduce and isolate crosstalk.
Crosstalk presents a particular problem in high frequency applications wherein as the frequency of transmission increases, crosstalk increases logarithmically. Thus, the need to shield twisted pairs increases with the need for greater transmission speed. For instance, a category 7 cable used for relatively high speed data transmission is required to meet specific performance standards for crosstalk isolation established by third party testing organizations. Therefore, in order to meet such performance standards, while providing greater transmission speed and throughput, methods of shielding and isolating twisted pairs become important for maintaining the quality of data transmission.
Various prior art methods attempt to meet standards for crosstalk isolation in high-speed data communications cable and include techniques and cable designs for physically separating twisted pairs and maintaining twisted pairs in fixed positions. In addition, prior art methods include individually shielding twisted pairs to insulate twisted pairs from crosstalk. Such shielding techniques typically include various techniques and shielding tapes for tape wrapping individual twisted pairs prior to cabling. Typically, tape wrapping involves wrapping a metal or metallized tape longitudinally or helically around a twisted pair. Such tape wrapping techniques cause a portion of the metal or tape to overlap upon itself as it is wound around the twisted pair to achieve a continuous wrap. The result is that areas along the twisted cable face a metal-to-nonmetal portion of the wrapping tape at the site of a tape overlap. Typically, shielding or wrapping tape comprises a conductive, often metallic, surface and a dielectric film, often plastic, surface such that the overlap created is a metal-to-film interface. Such overlaps are susceptible to signal leakage, interference and signal degradation as well as contribute to crosstalk between adjacent twisted pairs and proximate cables. In addition, individually wrapping twisted pairs is a lengthy operation and an additional step in manufacturing twisted pairs.
Therefore, it is desirable to provide a shielding tape and techniques for individually wrapping twisted pairs prior to cabling that overcomes the problems associated with the prior art described above. Such a shielding tape and techniques would reduce or eliminate the negative effects upon electrical properties and conductor performance associated with tape overlap and more particularly would isolate crosstalk. In addition it is desirable to provide a communications cable comprising a shielding tape for physically separating and electrically isolating individual insulated conductors contained therein to substantially reduce crosstalk between adjacent conductors situated within the cable as well as between the cable and other proximately located communications cables.